a) Field of the Invention
The invention is directed to a vacuum valve with a valve plate which is arranged at a valve rod and by means of which a valve opening in a valve housing can be closed. The vacuum valve has an actuation device by means of which the valve plate is movable from its open position initially into a position which is located opposite the valve opening, but which is lifted from the valve seat, and can then be pressed against the valve seat surrounding the valve opening. The actuation device comprises first and second piston-cylinder units.
b) Description of the Related Art
Vacuum valves of the plate valve type in which the valve opening is closed by a valve plate which is pressed against the valve seat surrounding the valve opening are known in many different embodiment forms.
A first common embodiment form of plate valves of the type mentioned above are slide valves. In order to close the valve, the valve plate is initially displaced linearly by an actuation device in a direction transverse to the sealing surface until it is in a position which is located opposite to the valve opening, but is lifted from the valve seat. Subsequently, a movement is carried out vertical to the sealing surface and in the direction of the longitudinal axis of the valve opening, so that the valve plate is pressed against the valve seat. This two-step movement process is required so that the seal which is made of an elastic material, e.g., Viton, is not exposed to shearing stress, which would lead to unacceptable wear. The second step of the closing movement is achieved in different ways in slide valves of the type mentioned above, for example, by means of lever mechanisms, rolling bodies which are guided in wedge-shaped gaps between the valve plate and a supporting plate, tilting elements, and so on. In order to prevent bending of the valve rod during the second movement step (movement vertical to the sealing surface or valve opening), a counterplate is usually provided which is moved simultaneously against a wall located opposite the valve seat. Slide valves of this type are known, for example, from U.S. Pat. No. 4,560,141 A, DE 32 09 217 C2, DE 32 24 387 C2 and U.S. Pat. No. 3,185,435 A.
In a special type of plate valve or slide valve, the second movement step, that is, the movement of the valve plate against the valve seat by a movement directed essentially vertical to the sealing surface, is carried out in that the valve rod is swiveled about a fulcrum. This fulcrum can be formed by pins or rollers which are arranged laterally at the valve rod and guided in guide grooves. Accordingly, the valve rod is constructed in this instance in the manner of a lever which is initially displaced linearly and is then tilted. Examples of valve constructions of this type are shown in U.S. Pat. No. 5,415,376 A, U.S. Pat. No. 5,641,149 A, U.S. Pat. No. 6,045,117 A, U.S. Pat. No. 5,934,646 A, U.S. Pat. No. 5,755,255 A, U.S. Pat. No. 6,082,706 A and U.S. Pat. No. 6,095,180 A. Another valve device of this type is known from DE 19 63 37 98 A1. In the latter reference, the first and second movement steps for closing the valve are carried out by means of separate piston-cylinder units.
Another vacuum valve with separate piston-cylinder units for carrying out the two movement steps is known from U.S. Pat. No. 6,056,266 A.
In another type of plate valve, there is no linear displacement of the valve plate in the first step of the valve plate movement; rather, the valve plate is swiveled along an arc in order to move the valve plate into the position located opposite the valve opening. For this purpose, the valve rod is suspended by its end opposite the valve plate at a shaft so as to be swivelable about an axis extending vertical to the valve face. The second step of the closing movement of the valve plate in the direction of the valve seat is carried out by a linear displacement of this shaft.
When separate piston-cylinder units are used for carrying out the first and second movement steps of the closing movement, it must be ensured that they are actuated in the correct sequence when closing the valve as well as when opening the valve in order to prevent damage to the valve. Sequence control devices for controlling pneumatic consumers in correct sequence are known. However, they are usually relatively complicated.
A primary object of the present invention is to provide a vacuum valve of the type mentioned above which is constructed in a simple manner and operates reliably.
According to the invention, this object is met by a vacuum valve comprising
a valve opening which is provided in a valve housing, has an axis oriented in the through-flow direction of the valve and is surrounded by a valve seat,
a valve plate which is arranged at at least one valve rod and by means of which the valve opening can be closed in the closed state of the valve,
at least a first piston-cylinder unit by means of which the valve plate is displaceable from its open position releasing the valve opening into a position which is located opposite the valve opening but is lifted from the valve seat,
at least a second piston-cylinder unit by means of which the valve plate can be moved toward the valve seat and pressed against it from its position which is located opposite the valve opening but is lifted from the valve seat, wherein
the first piston-cylinder unit has a closing cylinder space, wherein a force acting upon the valve plate in the direction of its position located opposite the valve opening is generated when the closing cylinder space is acted upon by pressure,
the second piston-cylinder unit has a closing cylinder space, wherein a force acting upon the valve plate in the direction of its position in which it is pressed against the valve seat is generated when the closing cylinder space is acted upon by pressure,
the closing cylinder space of the first piston-cylinder unit has a base, wherein the piston of the first piston-cylinder unit is located adjacent to this base in the position of the valve plate which completely releases the valve opening,
the closing cylinder space of the second piston-cylinder unit has a base, wherein the piston of the second piston-cylinder unit is located adjacent to this base in the position of the valve plate in which the latter is completely lifted from the valve seat,
a first connection line runs between said base of the first piston-cylinder unit and said base of the second piston-cylinder unit, wherein a check valve or non-return valve is arranged in the first connection line and closes when there is a pressure in the closing cylinder space of the first piston-cylinder unit that is greater than or equal to the pressure in the closing cylinder space of the second piston-cylinder unit, and
a pin or mandrel is provided at the piston of the second piston-cylinder unit, which mandrel releases the non-return valve when the valve plate is in the position in which it is completely lifted from the valve seat.
In this way, the movement steps are carried out in correct sequence when the vacuum valve is opened as will be explained in more detail in the description of the drawings with reference to an embodiment example.
In a preferred embodiment example of the invention, a recess is provided in the base of the second piston-cylinder unit, wherein a projection of the piston of the second piston-cylinder unit can be inserted into this recess in the position of the valve plate in which it is completely lifted from the valve seat, wherein a first control line opens into this recess, namely, in the area below the inserted projection which forms a piston surface. Further, the opening cylinder space of the first piston-cylinder unit (wherein a force acting upon the valve plate in the direction of its position which completely releases the valve opening is generated when this opening cylinder space is acted upon by pressure) and the opening cylinder space of the second piston-cylinder unit (wherein a force acting upon the valve plate in the direction of its position in which it is completely lifted from the valve seat is generated when this opening cylinder space is acted upon by pressure) are connected with one another by a second connection line into which a second control line opens. By means of this step, a very simply constructed sequence control arrangement can also be realized for the closing movement of the valve as will be explained in more detail in the description of the drawings with reference to an embodiment example.
The various features and constructions according to the invention are reproduced in the claims.
Further advantages and details of the invention are explained in the following with reference to the embodiment example shown in the drawing, further objects of the invention also following therefrom.